Polyarylene sulfide and process for producing the same

ABSTRACT

In a production process of a poly(arylene sulfide), a mixture containing an organic amide solvent, an alkali metal hydrosulfide and an alkali metal hydroxide in a proportion of 0.95 to 1.05 mol per mol of the alkali metal hydrosulfide is heated and dehydrated in a dehydration step. After the dehydration step, as needed, an alkali metal hydroxide and water are added to control the total number of moles of the alkali metal hydroxide, and the number of moles of water so as to amount to 1.00 to 1.09 per mol of a sulfur source including the alkali metal hydrosulfide existing in the system and to 0.5 to 2.0 per mol of the charged sulfur source, respectively. A polymerization step is conducted by a two-stage process.

TECHNICAL FIELD

The present invention relates to a production process of a poly(arylenesulfide) by subjecting a sulfur source and a dihalo-aromatic compound toa polymerization reaction in an organic amide solvent, and particularlyto a production process of a poly(arylene sulfide), by which an alkalimetal hydrosulfide and an alkali metal hydroxide can be used incombination as materials for a sulfur source to stably conduct apolymerization reaction, and polymers extremely low in the content ofbis(4-chlorophenyl) sulfide that is an impurity secondarily producedupon the polymerization reaction, excellent in reactivity to silanecoupling agents such as γ-aminopropyltriethoxysilane, little in volatilematter in a compound and good in color tone can be provided.

The present invention also relates to poly(arylene sulfides) low in thecontent of bis(4-chlorophenyl) sulfide. The present invention furtherrelates to poly(arylene sulfides) excellent in reactivity to silanecoupling agents such as γ-aminopropyltriethoxysilane.

BACKGROUND ART

Poly(arylene sulfides) (hereinafter abbreviated as “PASs”) representedby poly(phenylene sulfide) (hereinafter abbreviated as “PPS”) are anengineering plastics excellent in heat resistance, chemical resistance,flame retardancy, mechanical properties, electrical properties,dimensional stability and the like. The PASs are commonly used in widefields such as electrical and electronic equipments and automotiveequipments because they can be formed or molded into various kinds ofmolded or formed products, films, sheet, fibers, etc. by general meltprocessing techniques such as extrusion, injection molding andcompression molding.

As a typical production process of PAS, is known a process in which asulfur source is reacted with a dihalo-aromatic compound in an organicamide solvent such as N-methyl-2-pyrrolidone. There is known a method ofusing an alkali metal hydrosulfide and an alkali metal hydroxide incombination as materials for the sulfur source. However, this method isdifficult to set conditions for stably performing a polymerizationreaction. In addition, according to this method, difficulty isencountered on inhibition of side reactions, the content of volatilematter becomes great, and difficulty is encountered on reduction in thecontent of bis(4-chlorophenyl) sulfide that is an impurity due to agreat amount of the alkali metal hydroxide used upon the polymerizationreaction.

There has heretofore been proposed a production process of PAS, in whichan alkali metal hydrosulfide, an alkali metal hydroxide and apolyhalo-aromatic compound are reacted by 2 stages (for example,Japanese Patent Application Laid-Open Nos. 2-302436 and 5-271414). InJapanese Patent Application Laid-Open No. 2-302436, it is described thatthe amount of the alkali metal hydroxide used is within a range of 0.7to 1.3 mol, preferably 0.9 to 1.1 mol per mol of the alkali metalhydrosulfide. In Examples of Japanese Patent Application Laid-Open No.2-302436, is shown an experimental example that sodium hydroxide wasused in a proportion of 0.92 mol per mol of sodium hydrosulfide.Japanese Patent Application Laid-Open No. 5-271414 also disclose a liketechnical matter.

According to these processes, however, it is difficult to reduce thecontent of bis(4-chlorophenyl) sulfide and also to improve thereactivity to silane coupling agents. In addition, there is a tendencyto make it difficult to stably perform a polymerization reaction and tofail to produce a high-molecular weight polymer at high yield when themolar ratio of sodium hydroxide used to sodium hydrosulfide is low asshown in Examples of these documents. Japanese Patent ApplicationLaid-Open No. 2-302436 describes the fact that the amount of gasesgenerated is small, but does not show analytical results as to gascompositions.

There has been proposed a production process of poly(p-phenylene)sulfide, in which a molar ratio of an alkali metal hydroxide to analkali metal hydrosulfide is controlled to 0.80:1 to 0.98:1 to conductpolymerization by one stage (for example, Japanese Patent PublicationNo. 6-51792). According to this process, however, side reactions areeasy to occur, difficulty is encountered on stably performing apolymerization reaction, and moreover it is also difficult to reduce thecontent of bis(4-chlorophenyl) sulfide and to improve the reactivity tosilane coupling agents.

There has been proposed a production process of PAS, in which an alkalimetal hydroxide is used in a proportion amounting to at most 1 mol permol of an alkali metal hydrosulfide to conduct polymerization by onestage (for example, Japanese Patent Application Laid-Open No.2001-181394). There has also been proposed a production process of PASby one stage by using an alkali metal hydrosulfide and an alkali metalhydroxide to specify a molar ratio between the respective components(for example, Japanese Patent Application Laid-Open No. 2-160834). Therehas further been proposed a process for producing PAS by one stage bycontrolling the amount of an alkali metal hydroxide added to 0.3 to 4mol per mol of an alkali metal hydrosulfide (for example, JapanesePatent Publication No. 6-51793). However, these processes also involvethe same problems as in Japanese Patent Publication No. 6-51792.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a production processof a poly(arylene sulfide) extremely low in the content ofbis(4-chlorophenyl) sulfide that is an impurity secondarily producedupon a polymerization reaction, excellent in reactivity to silanecoupling agents such as γ-aminopropyltriethoxysilane (i.e.,aminosilane), little in volatile matter in a compound and good in colortone, by which an alkali metal hydrosulfide and an alkali metalhydroxide can be used as materials for a sulfur source to stably conducta polymerization reaction.

Another object of the present invention is to provide poly(arylenesulfides) low in the content of bis(4-chlorophenyl) sulfide. A furtherobject of the present invention is to provide poly(arylene sulfides)excellent in reactivity to silane coupling agents such asγ-aminopropyltriethoxysilane.

The present inventors have carried out an extensive investigation with aview toward achieving the above objects. As a result, the inventors haveconceived of a process comprising, in a dehydration step for controllingthe amount of water in a production process of PAS by polymerizing asulfur source and a dihalo-aromatic compound in an organic amidesolvent, heating and reacting a mixture containing an alkali metalhydroxide in a proportion of 0.95 to 1.05 mol per mol of an alkali metalhydrosulfide in the organic amide solvent to dehydrate the mixture,arranging a charging step of adding an alkali metal hydroxide and waterto the mixture remaining in the system after the dehydration step, asneeded, to control the total number of moles of the number of moles ofan alkali metal hydroxide formed with hydrogen sulfide formed upon thedehydration, the number of moles of the alkali metal hydroxide addedprior to the dehydration and the number of moles of the alkali metalhydroxide added after the dehydration, and the number of moles of waterso as to amount to 1.00 to 1.09 per mol of a sulfur source (chargedsulfur source) including the alkali metal hydrosulfide existing in thesystem after the dehydration and to 0.5 to 2.0 per mol of the chargedsulfur source, respectively, and further performing a polymerizationreaction by a specific two-stage process.

The process according to the present invention has a feature in that amolar ratio between the alkali metal hydrosulfide and alkali metalhydroxide charged in the dehydration step is controlled within a limitedspecific range, and a proportion of the alkali metal hydroxide to 1 molof the sulfur source is controlled within a specific limited range.Further, the process according to the present invention also has afeature in that a specific two-stage polymerization process is adopted.

According to the production process of the present invention, thepolymerization reaction can be stably performed, and inconvenientreactions such as thermal decomposition are inhibited. According to theproduction process of the present invention, there can be provided PAShaving a bis(4-chlorophenyl) sulfide content lower than 50 ppm.

According to the production process of the present invention, there canalso be provided PAS excellent in reactivity to a silane coupling agentas demonstrated by a ratio (MV2/MV1) of a melt viscosity value (MV2) ofthe PAS after a reaction with aminosilane to a melt viscosity value(MV1) before the reaction exceeds 2.0 as measured at a temperature of310° C. and a shear rate of 1,216 sec⁻¹.

According to the production process of the present invention, there canfurther be provided PAS which is markedly inhibited in coloring andlittle in volatile matter in a compound.

The present invention has been led to completion on the basis of thesefindings.

According to the present invention, there is provided a poly(arylenesulfide) having a bis(4-chlorophenyl) sulfide content lower than 50 ppmas determined by a gas chromatographic analysis in accordance with ameasuring method specified in the description of the presentapplication.

According to the present invention, there is also provided apoly(arylene sulfide) having a ratio (MV2/MV1) of a melt viscosity value(MV2) of the poly(arylene sulfide) after a reaction with aminosilane asspecified in the description of the present application to a meltviscosity value (MV1) before the reaction exceeding 2.0 as measured at atemperature of 310° C. and a shear rate of 1,216 sec⁻¹.

According to the present invention, there is further provided a processfor producing a poly(arylene sulfide) by polymerizing a sulfur sourceand a dihalo-aromatic compound in an organic amide solvent, whichcomprises the respective steps of:

-   (1) a dehydration step of heating and reacting a mixture containing    the organic amide solvent, an alkali metal hydrosulfide and an    alkali metal hydroxide in a proportion of 0.95 to 1.05 mol per mol    of the alkali metal hydrosulfide to discharge at least a part of a    distillate containing water from the interior of the system    containing the mixture to the exterior of the system,-   (2) a charging step of adding an alkali metal hydroxide and water to    the mixture remaining in the system after the dehydration step, as    needed, to control the total number of moles of the number of moles    of an alkali metal hydroxide formed with hydrogen sulfide formed    upon the dehydration, the number of moles of the alkali metal    hydroxide added prior to the dehydration and the number of moles of    the alkali metal hydroxide added after the dehydration, and the    number of moles of water so as to amount to 1.00 to 1.09 per mol of    a sulfur source (hereinafter referred to as “charged sulfur source”)    including the alkali metal hydrosulfide existing in the system after    the dehydration and to 0.5 to 2.0 per mol of the charged sulfur    source, respectively,-   (3) an first-stage polymerization step of adding a dihalo-aromatic    compound to the mixture to subject the sulfur source and the    dihalo-aromatic compound to a polymerization reaction at a    temperature of 170 to 270° C., thereby forming a prepolymer that a    conversion of the dihalo-aromatic compound is 50 to 98%, and-   (4) a second-stage polymerization step of controlling the amount of    water in the reaction system after the first-stage polymerization    step so as to bring about a state that water exists in a proportion    of more than 2.0 mol, but up to 10 mol per mol of the charged sulfur    source, and heating the reaction system to 245 to 290° C., thereby    continuing the polymerization reaction.

BEST MODE FOR CARRYING OUT THE INVENTION

1. Sulfur Source:

In the present invention, an alkali metal hydrosulfide is used as asulfur source. As examples of the alkali metal hydrosulfide, may bementioned lithium hydrosulfide, sodium hydrosulfide, potassiumhydrosulfide, rubidium hydrosulfide, cesium hydrosulfide and mixtures oftwo or more compounds thereof. The alkali metal hydrosulfide may be usedin any form of an anhydride, a hydrate and an aqueous solution. Amongthese, sodium hydrosulfide and lithium hydrosulfide are preferred inthat they are industrially available on the cheap. The alkali metalhydrosulfide is preferably used as an aqueous mixture (i.e., a mixturewith water having fluidity) such as an aqueous solution from theviewpoints of processing operation, weighing, etc.

In general, a small amount of an alkali metal sulfide is secondarilyproduced in a production process of the alkali metal hydrosulfide. Asmall amount of the alkali metal sulfide may be contained in the alkalimetal hydrosulfide used in the present invention. In this case, thetotal molar quantity of the alkali metal hydrosulfide and alkali metalsulfide becomes a charged sulfur source after a dehydration step.

Examples of the alkali metal hydroxide include lithium hydroxide, sodiumhydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide andmixtures of two or more compounds thereof. Among these, sodium hydroxideand lithium hydroxide are preferred in that they are industriallyavailable on the cheap. The alkali metal hydroxide is preferably used asan aqueous mixture such as an aqueous solution.

In the production process according to the present invention, examplesof water to be dehydrated in the dehydration step includes water ofhydration, a water medium of an aqueous solution and water secondarilyproduced in a reaction of the alkali metal hydrosulfide with the alkalimetal hydroxide, or the like.

2. Dihalo-aromatic Compound:

The dihalo-aromatic compound used in the present invention is adihalogenated aromatic compound having 2 halogen atoms directly bondedto the aromatic ring. Specific examples of the dihalo-aromatic compoundinclude o-dihalobenzene, m-dihalobenzene, p-dihalobenzene,dihalotoluene, dihalonaphthalene, methoxy-dihalobenzene, dihalobiphenyl,dihalobenzoic acid, dihalodiphenyl ether, dihalodiphenyl sulfone,dihalodiphenyl sulfoxide and dihalodiphenyl ketone.

Here, the halogen atom means each of fluorine, chlorine, bromine andiodine atoms, and 2 halogen atoms in the same dihalo-aromatic compoundmay be the same or different from each other. These dihalo-aromaticcompounds may be used either singly or in any combination thereof.

The charged amount of the dihalo-aromatic compound is generally 0.90 to1.50 mol, preferably 0.95 to 1.20 mol, more preferably 1.00 to 1.09 molper mol of the sulfur source (alkali metal sulfide and/or alkali metalhydrosulfide) remaining in the system after the dehydration step.

3. Molecular Weight Control Agent, Branching or Crosslinking Agent:

In order to, for example, form a terminal of a specific structure in aPAS formed or regulate a polymerization reaction or a molecular weight,a monohalo-compound (may not be always an aromatic compound) may be usedin combination. In order to form a branched or crosslinked polymer, apolyhalo-compound (may not be always an aromatic compound), to which atleast 3 halogen atoms are bonded, an active hydrogen-containinghalogenated aromatic compound, a halogenated aromatic nitro compound orthe like may also be used in combination. A preferable example of thepolyhalo-compound as a branching or crosslinking agent includestrihalobenzene.

4. Organic Amide Solvent:

In the present invention, an organic amide solvent that is an aproticpolar organic solvent is used as a solvent for the dehydration reactionand polymerization reaction. The organic amide solvent is preferablystable to an alkali at a high temperature.

Specific examples of the organic amide solvent include amide compoundssuch as N,N-dimethylformamide and N,N-dimethylacetamide;N-alkylcaprolactam compounds such as N-methyl-ε-caprolactam;N-alkylpyrrolidone compounds or N-cycloalkylpyrrolidone compound such asN-methyl-2-pyrrolidone and N-cyclohexyl-2-pyrrolidone;N,N-dialkyl-imidazolidinone compounds such as1,3-dialkyl-2-imidazolidinones; tetraalkylurea compounds such astetramethylurea; and hexaalkylphosphoric triamide compounds such ashexamethylphosphoric triamide. These organic amide solvents may be usedeither singly or in any combination thereof.

Among these organic amide solvents, N-alkyl-pyrrolidone compounds,N-cycloalkylpyrrolidone compounds, N-alkylcaprolactam compounds andN,N-dialkyl-imidazolidinone compounds are preferred, andN-methyl-2-pyrrolidone, N-methyl-ε-caprolactam and1,3-dialkyl-2-imidazolidinones are particularly preferably used.

The amount of the organic amide solvent used in the polymerizationreaction in the present invention is generally within a range of 0.1 to10 kg per mol of the sulfur source.

5. Polymerization Aid:

In order to promote the polymerization reaction to obtain a PAS having ahigh polymerization degree in a short period of time, various kinds ofpolymerization aids may be used in the present invention as needed.Specific examples of the polymerization aids include metal salts oforganic sulfonic acids, lithium halides, metal salts of organiccarboxylic acids and alkali metal salts of phosphoric acid. Among these,metal salts of organic carboxylic acids are particularly preferredbecause they are cheap.

The amount of the polymerization aid used varies according to the kindof the compound used. However, it is generally within a range of 0.01 to10 mol per mol of the charged sulfur source.

6. Dehydration Step:

A dehydration step is arranged as a preliminary step for apolymerization step to control the amount of water in the reactionsystem. The dehydration step is performed by a process comprisingheating and reacting a mixture containing an organic amide solvent, analkali metal hydrosulfide and an alkali metal hydroxide, desirably,under an inert gas atmosphere and discharging water outside the systemby distillation.

In the present invention, the mixture containing the organic amidesolvent, the alkali metal hydrosulfide and the alkali metal hydroxide ina proportion of 0.95 to 1.05 mol per mol of the alkali metalhydrosulfide is heated and reacted to discharge at least a part of adistillate containing water from the interior of the system containingthe mixture to the exterior of the system.

If a molar ratio of the alkali metal hydroxide to 1 mol of the chargedalkali metal hydrosulfide in this step is too small, the amount of asulfur component (hydrogen sulfide) volatilized out in the dehydrationstep becomes great, which tends to incur reduction in productivity dueto lowering of the amount of the charged sulfur source or cause abnormalreactions and deterioration of a PAS formed due to increase in apolysulfide component in the charged sulfur source remaining after thedehydration. If a molar ratio of the alkali metal hydroxide to 1 mol ofthe charged alkali metal hydrosulfide is too large, in some cases,change in properties of the organic amide solvent may be increased,difficulty may be encountered on stably performing the polymerizationreaction, or the yield and quality of a PAS formed may be deteriorated.A preferable molar ratio of the alkali metal hydroxide to 1 mol of thecharged alkali metal hydrosulfide in this step is 0.96 to 1.04.

In many cases, a small amount of an alkali metal sulfide is contained inan alkali metal hydrosulfide, so that the amount of the sulfur sourceinvolves a total of the alkali metal hydrosulfide and the alkali metalsulfide. No problem arises as to a raw material for PAS even if thealkali metal hydrosulfide contains the alkali metal sulfide. However,the content thereof is preferably as low as possible for the purpose ofproducing a high-quality PAS according to the present invention. Evenwhen a small amount of the alkali metal sulfide is mixed in, the molarratio to the alkali metal hydroxide is calculated out on the basis ofthe content (analytical value) of the alkali metal hydrosulfide in thepresent invention to regulate the molar ratio.

In the dehydration step, the dehydration is conducted until the contentof water comprising water of hydration (water of crystallization), awater medium, secondarily produced water, etc. is lowered within a rangeof necessary amounts. In the dehydration step, the dehydration isconducted until the water content in the polymerization reaction systemis reduced to 0.5 to 2.0 mol per mol of the sulfur source. When thewater content has become too low in the dehydration step, water may beadded prior to the polymerization step to regulate the water content toa desired value.

The charging of these raw materials into a reaction vessel is conductedwithin a temperature range of generally from ordinary temperature (5 to35° C.) to 300° C., preferably from ordinary temperature to 200° C. Thecharging of the raw materials may not be in order, and the respectiveraw materials may be additionally charged in the course of thedehydration process. An organic amide solvent is used as a solvent usedin the dehydration step. This solvent is preferably the same as theorganic amide solvent used in the polymerization step, andN-methyl-2-pyrrolidone is particularly preferred. The amount of theorganic amide solvent used is generally about 0.1 to 10 kg per mol ofthe sulfur source charged in the reaction vessel.

The dehydration process is conducted by heating the mixture aftercharging the raw materials into the reaction vessel in a temperaturerange of generally up to 300° C., preferably 100 to 250° C. forgenerally 15 minutes to 24 hours, preferably 30 minutes to 10 hours.Heating methods include a method of retaining a fixed temperature, amethod of raising the temperature either stepwise or continuously and amethod of combining both methods. The dehydration step is conducted by,for example, a batch system, a continuous system or a combined systemthereof.

An apparatus for conducting the dehydration step may be the same as areaction vessel (reactor) used in the subsequent polymerization step ordifferent from it. A material of the apparatus is preferably a corrosionresistant material such as titanium. In the dehydration step, a part ofthe organic amide solvent is generally discharged together with wateroutside the reaction vessel. At that time, hydrogen sulfide isdischarged as a gas outside the system.

In the dehydration step, it is considered that the alkali metalhydroxide reacts with the organic amide solvent by the heat treatment toform an alkali metal alkylaminoalkanoate, and the alkali metalhydrosulfide exists in the system in the form of a complex with thealkali metal alkylaminoalkanoate. On the other hand, a part of thealkali metal hydrosulfide reacts with water to form hydrogen sulfide andan alkali metal hydroxide, and the hydrogen sulfide formed is dischargedoutside the system. The discharge of hydrogen sulfide outside the systemis directly linked with the weight loss of the sulfur source in thesystem. Accordingly, it is important to measure the amount of hydrogensulfide volatilized out in the dehydration step to exactly calculate outthe amount of the sulfur source remaining in the system in that a molarratio to the alkali metal hydroxide or dihalo-aromatic compound isregulated.

7. Charging Step:

In the present invention, as needed, an alkali metal hydroxide and waterare added to the mixture remaining in the system after the dehydrationstep to control the total number of moles of the number of moles of analkali metal hydroxide formed with hydrogen sulfide formed upon thedehydration, the number of moles of the alkali metal hydroxide addedprior to the dehydration and the number of moles of the alkali metalhydroxide added after the dehydration so as to amount to 1.00 to 1.09per mol of the sulfur source (charged sulfur source) including thealkali metal hydrosulfide existing in the system after the dehydrationand the number of moles of water so as to amount to 0.5 to 2.0 per molof the charged sulfur source, respectively.

Here, the amount of the charged sulfur source is calculated out inaccordance with an equation, [Charged sulfur source]=[Total moles ofsulfur charged]−[Moles of sulfur volatilized out after dehydration].

When hydrogen sulfide is volatilized out in the dehydration step, analkali metal hydroxide is formed by an equilibrium reaction and comes toremain in the system. Accordingly, it is necessary to exactly graspthese amounts to determine a molar ratio of the alkali metal hydroxideto the sulfur source in the charging step.

If the molar ratio of the alkali metal hydroxide to 1 mol of the sulfursource is too high, change in properties of the organic amide solventmay be increased, or abnormal reactions or decomposition reactions tendto occur upon polymerization. In addition, the lowering of the yield andquality of a PAS formed is often caused. The molar ratio of the alkalimetal hydroxide to 1 mol of the sulfur source is preferably 1.01 to 1.08mol, more preferably 1.015 to 1.075 mol. It is preferred to conduct thepolymerization reaction slightly in excess of the alkali metal hydroxidein that the polymerization reaction is stably performed to obtain ahigh-quality PAS.

8. Polymerization Step:

The polymerization step is conducted by charging a dihalo-aromaticcompound into the mixture after completion of the dehydration step andheating the sulfur source and the dihalo-aromatic compound in an organicamide solvent. When another polymerization vessel than the reactionvessel used in the dehydration step is used, the mixture after thedehydration step and the dihalo-aromatic compound are charged into thepolymerization vessel. After the dehydration step and before thepolymerization step, the amounts of the organic amide solvent andcoexisting water may be controlled as needed. Before the polymerizationstep or during the polymerization step, a polymerization aid and otheradditives may be mixed.

The mixing of the mixture obtained after completion of the dehydrationstep with the dihalo-aromatic compound is conducted within a temperaturerange of generally from 100 to 350° C., preferably from 120 to 330° C.When the respective components are charged into the polymerizationvessel, no particular limitation is imposed on the order of charging,and both components are charged in small portions or at a time.

The polymerization reaction is generally conducted by a two-stageprocess at a temperature ranging from 170 to 290° C. As a heatingmethod, is used a method of retaining a fixed temperature, a method ofraising the temperature either stepwise or continuously or a combinationof both methods. The polymerization reaction time is within a range ofgenerally from 10 minutes to 72 hours, desirably from 30 minutes to 48hours. The amount of the organic amide solvent used in thepolymerization step is within a range of generally from 0.1 to 10 kg,preferably from 0.15 to 1 kg per mol of the charged sulfur sourceexisting in the polymerization step. The amount may be changed in thecourse of the polymerization reaction so far as it falls within thisrange.

The water content upon the beginning of the polymerization reaction iscontrolled within a range of 0.5 to 2.0 mol per mol of the chargedsulfur source. It is preferable to increase the water content in thecourse of the polymerization reaction.

In the production process according to the present invention, thepolymerization reaction is conducted in the polymerization step by an atleast two-stage polymerization process comprising:

-   (1) a first-stage polymerization step of heating a reaction mixture    containing the organic amide solvent, the sulfur source, the    dihalo-aromatic compound and the alkali metal hydroxide of the    specified molar ratio to 170 to 270° C. in the presence of water in    an amount of 0.5 to 2.0 mol per mol of the charged sulfur source to    conduct a polymerization reaction, thereby forming a prepolymer that    a conversion of the dihalo-aromatic compound is 50 to 98%, and-   (2) a second-stage polymerization step of controlling the amount of    water in the reaction system so as to bring about a state that water    exists in a proportion of more than 2.0 mol, but up to 10 mol per    mol of the charged sulfur source, and heating the reaction system to    245 to 290° C., thereby continuing the polymerization reaction.

In the first-state polymerization step, it is desirable to form aprepolymer having a melt viscosity of 0.5 to 30 Pa·s as measured at atemperature of 310° C. and a shear rate of 1,216 sec⁻¹.

Water may be added at a second stage of the polymerization reaction orupon completion thereof to increase the water content for the purpose oflowering the contents of common salt secondarily produced and impuritiesin the polymer formed or collecting the polymer in the form ofparticles. The polymerization reaction system may be a batch system, acontinuous system or a combination of both systems. In the batch-wisepolymerization, 2 or more reaction vessels may be used for the purposeof shortening the polymerization cycle time.

9. Post Treatment Step:

In the production process according to the present invention, a posttreatment after the polymerization reaction may be conducted inaccordance with a method known per se in the art. For example, aftercompletion of the polymerization reaction, a product slurry cooled isseparated by filtration as it is or after diluted with water or thelike, and the resulting filter cake is washed and filtered repeatedly,whereby PAS can be collected. According to the production process of thepresent invention, a granular polymer can be formed, so that thegranular polymer is preferably separated from the reaction mixture by amethod of sieving the polymer by means of a screen because the polymercan be easily separated from by-products, oligomers, etc. The productslurry may be subjected to sieving as it is in a high-temperature state,thereby collecting the polymer.

After the separation (sieving) by filtration, the PAS is preferablywashed with the same organic amide solvent as the polymerizationsolvent, or an organic solvent such as a ketone (for example, acetone)or an alcohol (for example, methanol). The PAS may be washed with hotwater. The PAS formed may also be treated with an acid or a salt such asammonium chloride.

10. PAS:

According to the production process of the present invention, there canbe provided a PAS having a bis(4-chlorophenyl) sulfide content lowerthan 50 ppm, preferably not higher than 40 ppm, more preferably nothigher than 30 ppm as determined in accordance with a measuring method(described in Examples) specified in the description of the presentapplication. When the bis(4-chlorophenyl) sulfide content amounts to atleast 50 ppm, the volatile matter content becomes excessive when acompound making use of such a PAS is injection-molded, so that theresulting molded product tends to cause defects at its appearance, orthe amount of impurities attached to a mold increases to markedly lowerworkability upon molding and processing. In the present invention, ppmis based on the weight.

According to the production process of the present invention, there canalso be provided a PAS having a ratio (MV2/MV1) of a melt viscosityvalue (MV2) of the PAS after a reaction (described in Examples) withaminosilane (i.e., γ-aminopropyltriethoxysilane) as specified in thedescription of the present application to a melt viscosity value (MV1)before the reaction of higher than 2.0, preferably at least 2.1 asmeasured at a temperature of 310° C. and a shear rate of 1,216 sec⁻¹.The upper limit of this ratio is generally about 3.0. A higher ratioindicates that the reactivity of the PAS to a silane coupling agent ishigher.

When the reactivity to aminosilane is high, a viscosity in a moltenstate of a composition composed of the PAS and aminosilane becomes high,the relation of the viscosity to the shear rate differs from PAS alone,such effects that occurrence of burr in melt molding is reduced arebrought about, and selection latitude of melt processing conditions canbe widened. If MV2/MV1 is lower than 2, such a polymer tends to lessenthe effect to develop such properties. When the production process ofPAS according to the present invention is used, MV2/MV1 may also bestabilized. When MV2/MV1 varies, the melt viscosity of a compositioncomprising such a PAS and aminosilane tends to vary. Thus, such apolymer is not preferred. Accordingly, it is desirable to control theratio within a fixed range, and the present invention can also meet therequirement.

The PAS obtained by the production process according to the presentinvention is good in color tone, and its yellow index (YI) is generallyat most 10, preferably at most 8, more preferably at most 7, oftenwithin a range of 5 to 6. A compound of the PAS obtained by theproduction process according to the present invention is little in theamount of volatile matter generated and is also suitable for use infields of electronic equipments and the like, in which inhibition ofvolatile matter is desired.

After the second-stage polymerization step, the PAS according to thepresent invention, which is obtained by collecting from the reactionmixture, has a melt viscosity higher than the melt viscosity of theprepolymer obtained in the first-stage polymerization step as measuredat a temperature of 310° C. and a shear rate of 1,216 sec⁻¹. Noparticular limitation is imposed on the melt viscosity (temperature:310° C., shear rate: 1,216 sec⁻¹) of the PAS according to the presentinvention. However, it is within a range of preferably from 30 to 800Pa·s, more preferably from 40 to 500 Pa·s.

The PAS obtained by the production process according to the presentinvention may be molded or formed into various injection-molded productsor extruded products such as sheets, films, fibers and pipes eithersingly or by incorporating various kinds of inorganic fillers, fibrousfillers and/or various kinds of synthetic resins, if desired, as it isor after oxidized and crosslinked. The PAS is particularly preferablyPPS.

EXAMPLES

The present invention will hereinafter be described more specifically bythe following Examples and Comparative Examples. Physical properties andthe like were measured in accordance with the following respectivemethods.

(1) Yield:

Assuming that all the available sulfur component existing in a reactionvessel after a dehydration step was converted to a polymer, the weight(theoretical amount) of that polymer was used as a reference value tocalculate out a proportion (% by weight) of the weight of a polymeractually collected to the reference value as a yield of the polymer.

(2) Melt Viscosity:

A melt viscosity was measured by using about 20 g of a dry polymer bymeans of Capirograph 1-C (manufactured by Toyo Seiki Seisakusho, Ltd.).At this time, a flat die of 1 mm in diameter and 10 mm in length wasused as a capillary, and the temperature was set to 310° C. After thepolymer sample was placed in the apparatus and held for 5 minutes, themelt viscosity was measured at a shear rate of 1,216 sec⁻¹.

(3) Color Tone (Yellow Index):

A polymer was pressed under 15 MPa for 1 minute by means of an electricpower press to prepare tablets. The tablets were used as a measurementsample to measure a color tone by means of TC-1800 (manufactured byTokyo Denshoku Gijutsu Center) in accordance with a reflected lightmeasuring method under conditions of standard light C, a visual field of20 and a calorimetric system. Prior to the measurement, the apparatuswas calibrated by a standard white plate. The measurement was conductedat 3 points as to each sample, and an average value thereof wascalculated out. The color tone was indicated by a yellow index (YI)value.

(4) Reactivity of Polymer:

To 100 parts by weight of a polymer was added 0.8 parts by weight ofγ-aminopropyltriethoxysilane (hereinafter abbreviated as “aminosilane”),and they were well blended. Thereafter, 20 g of the blend was taken outto measure a melt viscosity value thereof under the same melt viscositymeasuring conditions as described above. The reactivity of the polymerwas indicated by a ratio to a melt viscosity value of the polymer, towhich no aminosilane was added, under the same conditions. In otherwords, the reactivity of the polymer was evaluated by a ratio[(MV2)/(MV1); increase ratio of melt viscosity] of the melt viscosityvalue (MV2) of the blend of the polymer and aminosilane to the meltviscosity value (MV1) of the polymer. A higher ratio indicates that thereactivity of the polymer is higher.

(5) Determination of bis(4-chlorophenyl) sulfide:

In a NEG tube (10 mm in diameter×75 mm) is taken 30 mg of a dry polymer,and the tube is set in a Curie point head space sampler of JHS-100(manufactured by Japan Analytical Industry Co., Ltd.). The apparatus isheated at 180° C. for 30 minutes and at 330° C. for 15 minutes to causevolatile matter to pass through a trap vessel with built-in glass woolat 40° C. under a helium stream, thereby adsorbing and collecting it.The trap vessel is then cooled to room temperature and further heated at360° C. for 10 seconds to desorb the volatile matter, which is subjectedto gas chromatographic analysis using helium gas as it is, therebydetermining a volatile component.

<Conditions of Gas Chromatographic Analysis>

Apparatus: Hitachi G-3000,

Temperature of vaporizing chamber: 300° C.,

Column: HP-5 [0.32 mm in diameter×25 m; df (film thickness)=0.25 μm],

Column temperature: After holding at 60° C. for 5 minutes, raising thetemperature to 300° C. at a heating rate of 8° C./min and holding atthat temperature for 10 minutes,

Detector: FID (flame thermionic detector), 310° C.

Carrier gas: Helium, 2.5 ml/min,

Split ratio: 1/14.6, and

Determination: Determined from a calibration curve usingbis(4-chlorophenyl) sulfide synthesized.

(6) Volatilized Deposit Component of Compound:

After 60% by weight of a dry polymer, 39.8% by weight of a fibrousfiller (glass fiber having a diameter of 13 μm) and 0.2% by weight of alubricant were mixed for 5 minutes, the resultant mixture was melted andkneaded by a twin-screw extruder the cylinder temperature of which was320° C., thereby preparing pellets. Ten grams of the pellets thusprepared were weighed and taken in a test tube having a diameter of 10mm. A piece of SKD11 metal of 8-mm square (thickness: 2 mm) was placedon a stack of the pellets, and the test tube was sealed with a siliconstopper. The test tube was then put in an aluminum block bath and heatedat 340° C. for 4 hours. A volatilized deposit on the metal piece beforeand after the test was visually observed to make a judgment inaccordance with the following standard.

A: No deposit is observed,

B: Deposit is extremely slightly observed,

C: Deposit is observed, and

D: Deposit is markedly observed.

Example 1

1. Dehydration Step:

A 20-liter autoclave (reactor) made of titanium was charged with 2,000 gof an aqueous solution [sulfur (S) content: 22.43 mol; analytical valueof NaSH by a neutralization titration method: 61.48% by weight (21.93mol); sodium sulfide (Na₂S) content: 0.50 mol] of sodium hydrosulfide(NaSH) having an analytical value of 62.87% by weight by means ofiodimetry, 1,200 g of a 74.69% by weight aqueous solution (NaOH content:22.41 mol) of sodium hydroxide (NaOH) and 6,700 g ofN-methyl-pyrrolidone (hereinafter abbreviated as “NMP”). Assuming that asulfur source composed of sodium hydrosulfide and sodium sulfide isindicated as “S”, NaOH/NaSH before dehydration is 1.02 (mol/mol), andNaOH/S is 1.00 (mol/mol).

After purged with nitrogen gas, the contents were gradually heated to200° C. over 3.5 hours with stirring to distill off 940.0 g of water and1589.6 g of NMP. At this time, 0.31 mol of hydrogen sulfide (H₂S) wasvolatilized out. Accordingly, an available S content in the reactorafter the dehydration step was 22.12 mol. The amount of H₂S volatilizedout corresponded to 1.39 mol % based on the charged S content.

2. Charging Step:

After the dehydration step, the reactor containing 22.12 mol of theavailable S was cooled to 150° C., 3,299 g [p-dichlorobenzene(hereinafter abbreviated as “pDCB”)/available S=1.015 (mol/mol)] ofpDCB, 3,736 g of NMP and 118 g [total water content in thereactor/available S=1.50 (mol/mol)] of water were added, and 8.2 g ofNaOH having a purity of 97% was added in such a manner that (NaOH in thereactor/available S) is 1.05 (mol/mol). NaOH (0.62 mol) formed byvolatilization of H₂S is contained in the reactor.

3. Polymerization Step:

While a stirrer installed in the reactor was operated at 250 rpm, areaction was conducted at 220° C. for 1 hour, and the reaction mixturewas then heated to 230° C. over 30 minutes to conduct a reaction at 230°C. for 1.5 hours (first-stage polymerization step). Thereafter, thenumber of revolutions of the stirrer was increased to 400 rpm, 517.5 gof water was charged under pressure [total water content in thereactor/available S=2.80 (mol/mol)] while continuing the stirring, andthe contents were heated to 260° C. to conduct a reaction for 5.0 hours(second-stage polymerization step).

4. Post Treatment Step:

After completion of the reaction, the reaction mixture was cooled nearto room temperature, and the reaction mixture was sifted through ascreen of 100 mesh to collect a granular polymer. The thus-separatedpolymer was washed twice with acetone and additionally 3 times withwater to obtain a washed polymer. This washed polymer was immersed in a0.6% by weight aqueous solution of acetic acid to treat the polymer at40° C. for 40 minutes, and the thus-treated polymer was then washed withwater. The granular polymer was dried at 105° C. for 3 hours. The yieldof the granular polymer thus obtained was 90%, and its melt viscositywas 145 Pa·s. The polymerization conditions and the measured results ofphysical properties are shown in Tables 1 and 2.

Example 2

Charging was conducted in the same manner as in Example 1 except thatthe amount of the aqueous solution of sodium hydroxide (NaOH) chargedwas changed from 1,200 g to 1,150 g. Accordingly, NaOH/NaSH beforedehydration was 0.98 (mol/mol), and NaOH/S is 0.96 (mol/mol). In thedehydration step, dehydration was conducted under the same conditions asin Example 1. As a result, 935.0 g of water and 1567.3 g of NMP weredistilled off, and 0.34 mol of H₂S was volatilized out. The available Scontent in the reactor after the dehydration step was 22.09 mol. Theamount of H₂S volatilized out corresponded to 1.52 mol % based on thecharged S content.

Thereafter, 3,296 g [pDCB/available S=1.015 (mol/mol)] of pDCB, 3,703 gof NMP, 125.7 g [total water content in the reactor/available S=1.50(mol/mol)] of water and 15.8 g [NaOH in the reactor/available S=1.02(mol/mol)] of NaOH having a purity of 97% were added in the same manneras in Example 1 to conduct first-stage polymerization. Subsequently,516.9 g of water was charged under pressure [total water content in thereactor/available S=2.80 (mol/mol)] to conduct second-stagepolymerization. After completion of the polymerization, a polymer wascollected in the same manner as in Example 1. The yield of the granularpolymer thus obtained was 90%, and its melt viscosity was 125 Pa·s. Thepolymerization conditions and the measured results of physicalproperties are shown in Tables 1 and 2.

Example 3

Charging was conducted in the same manner as in Example 1 except thatthe amount of the aqueous solution of sodium hydroxide (NaOH) chargedwas changed from 1,200 g to 1,220 g. Accordingly, NaOH/NaSH beforedehydration was 1.04 (mol/mol), and NaOH/S is 1.02 (mol/mol). In thedehydration step, dehydration was conducted under the same conditions asin Example 1. As a result, 935.2 g of water and 1595.0 g of NMP weredistilled off, and 0.31 mol of H₂S was volatilized out. The available Scontent in the reactor after the dehydration step was 22.05 mol. Theamount of H₂S volatilized out corresponded to 1.69 mol % based on thecharged S content.

Thereafter, 3,274 g [pDCB/available S=1.010 (mol/mol)] of pDCB, 3,715 gof NMP, 108.5 g [total water content in the reactor/available S=1.50(mol/mol)] of water and 15.6 g [NaOH in the reactor/available S=1.075(mol/mol)] of NaOH having a purity of 97% were added in the same manneras in Example 1 to conduct first-stage polymerization while continuouslyheating the contents from 220° C. to 260° C. over 1.5 hours.Subsequently, 516.0 g of water was charged under pressure [total watercontent in the reactor/available S=2.80 (mol/mol)] to conductsecond-stage polymerization. After completion of the polymerization, apolymer was collected in the same manner as in Example 1. The yield ofthe granular polymer thus obtained was 88%, and its melt viscosity was110 Pa·s. The polymerization conditions and the measured results ofphysical properties are shown in Tables 1 and 2.

Comparative Example 1

Charging was conducted in the same manner as in Example 1 except thatthe amount of the aqueous solution of sodium hydroxide (NaOH) chargedwas changed from 1,200 g to 1,000 g. Accordingly, NaOH/NaSH beforedehydration was 0.85 (mol/mol), and NaOH/S is 0.83 (mol/mol). In thedehydration step, dehydration was conducted under the same conditions asin Example 1. As a result, 965.8 g of water and 1513.5 g of NMP weredistilled off, and 0.40 mol of H₂S was volatilized out. The available Scontent in the reactor after the dehydration step was 22.03 mol. Theamount of H₂S volatilized out corresponded to 1.78 mol % based on thecharged S content.

Thereafter, 3,287 g of pDCB and 3,625 g of NMP were added in such amanner that (pDCB/available S) is 1.015 (mol/mol), 195.0 g of water wasadded in such a manner that (total water content in thereactor/available S) is 1.50 (mol/mol), and 10.6 g of NaOH having apurity of 97% was added in such a manner that (NaOH in thereactor/available S) is 0.90 (mol/mol), thereby conducting first-stagepolymerization in the same manner as in Example 1. Subsequently, 515.5 gof water was charged under pressure in such a manner that (total watercontent in the reactor/available S) is 2.80 (mol/mol), therebyconducting second-stage polymerization. After completion of thepolymerization, a reaction product was decomposed, and so no polymer wascollected. The polymerization conditions and the results are shown inTables 1 and 2.

Comparative Example 2

Charging was conducted in the same manner as in Example 1 except thatthe amount of the aqueous solution of sodium hydroxide (NaOH) chargedwas changed from 1,200 g to 1,080 g. Accordingly, NaOH/NaSH beforedehydration was 0.92 (mol/mol), and NaOH/S is 0.90 (mol/mol). In thedehydration step, dehydration was conducted under the same conditions asin Example 1. As a result, 944.4 g of water and 1545.3 g of NMP weredistilled off, and 0.38 mol of H2S was volatilized out. The available Scontent in the reactor after the dehydration step was 22.05 mol. Theamount of H₂S volatilized out corresponded to 1.69 mol % based on thecharged S content.

Thereafter, 3,290 g of pDCB and 3,665 g of NMP were added in such amanner that (pDCB/available S) is 1.015 (mol/mol), 153.1 g of water wasadded in such a manner that (total water content in thereactor/available S) is 1.50 (mol/mol), and 41.5 g of NaOH having apurity of 97% was added in such a manner that (NaOH in thereactor/available S) is 1.0 (mol/mol), thereby conducting first-stagepolymerization in the same manner as in Example 1. Subsequently, 516.0 gof water was charged under pressure in such a manner that (total watercontent in the reactor/available S) is 2.80 (mol/mol), therebyconducting second-stage polymerization. After completion of thepolymerization, a polymer was collected in the same manner as inExample 1. The yield of the granular polymer thus obtained was 90%, andits melt viscosity was 90 Pa·s. The polymerization conditions and themeasured results of physical properties are shown in Tables 1 and 2.

Comparative Example 3

Charging was conducted in the same manner as in Example 1 except thatthe amount of the aqueous solution of sodium hydroxide (NaOH) chargedwas changed from 1,200 g to 1,220 g. Accordingly, NaOH/NaSH beforedehydration was 1.04 (mol/mol), and NaOH/S is 1.02 (mol/mol). In thedehydration step, dehydration was conducted under the same conditions asin Example 1. As a result, 930.3 g of water and 1590.7 g of NMP weredistilled off, and 0.44 mol of H₂S was volatilized out. The available Scontent in the reactor after the dehydration step was 21.99 mol. Theamount of H₂S volatilized out corresponded to 1.96 mol % based on thecharged S content.

Thereafter, 3,281 g of pDCB and 3,687 g of NMP were added in such amanner that (pDCB/available S) is 1.015 (mol/mol), 104.1 g of water wasadded in such a manner that (total water content in thereactor/available S) is 1.50 (mol/mol), and 19.5 g of NaOH having apurity of 97% was added in such a manner that (NaOH in thereactor/available S) is 1.100 (mol/mol), thereby conducting first-stagepolymerization in the same manner as in Example 1. Subsequently, 514.6 gof water was charged under pressure in such a manner that (total watercontent in the reactor/available S) is 2.80 (mol/mol), therebyconducting second-stage polymerization. After completion of thepolymerization, a polymer was collected in the same manner as inExample 1. The yield of the granular polymer thus obtained was 70%, andits melt viscosity was 90 Pa·s. The polymerization conditions and themeasured results of physical properties are shown in Tables 1 and 2.

Comparative Example 4

Charging was conducted in the same manner as in Example 1 except that552 g of sodium acetate was added, thereby conducting dehydration. As aresult, 935.3 g of water and 1590.3 g of NMP were distilled off, and0.31 mol of H₂S was volatilized out. The available S content in thereactor after the dehydration step was 22.12 mol. The amount of H₂Svolatilized out corresponded to 1.38 mol % based on the charged Scontent. After the dehydration step, 3,300 g of [pDCB/available S=1.015(mol/mol)] of pDCB and 3,738 g of NMP were added, and neither water norNaOH was added, so that (total water content in the reactor/available S)was 1.22 (mol/mol), and (NaOH in the reactor/available S) was 1.041(mol/mol).

Thereafter, in a polymerization step, a polymerization reaction wasconducted at 220° C. for 2 hours and then at 260° C. for 5 hours. Aftercompletion of the polymerization, a polymer was collected in the samemanner as in Example 1. The yield of the granular polymer thus obtainedwas 85%, and its melt viscosity was 130 Pa·s. The polymerizationconditions and the measured results of physical properties are shown inTables 1 and 2.

Comparative Example 5

Charging and dehydration were conducted in the same manner as inExample 1. As a result, 941.5 g of water and 1601.0 g of NMP weredistilled off, and 0.31 mol of H₂S was volatilized out. The available Scontent in the reactor after the dehydration step was 22.12 mol. Theamount of H₂S volatilized out corresponded to 1.38 mol % based on thecharged S content. Since 3,300 g of [pDCB/available S=1.015 (mol/mol)]of pDCB and 3,749 g of NMP were added, and neither water nor NaOH wasadded, (total water content in the reactor/available S) was 1.20(mol/mol), and (NaOH in the reactor/available S) was 1.041 (mol/mol).

Thereafter, in a polymerization step, a polymerization reaction wasconducted at 220° C. for 2 hours and then at 260° C. for 5 hours. Aftercompletion of the polymerization, a polymer was collected by a flashingmethod while holding the reaction mixture at a temperature of 260° C.The polymer thus obtained was washed 5 times with water. The yield ofthe polymer was 95%, and its melt viscosity was 95 Pa·s. Thepolymerization conditions and the measured results of physicalproperties are shown in Tables 1 and 2. TABLE 1 Before First-stagepolymerization dehydration NaOH in NaOH/S NaOH/NaSH NMP/S pDCB/S H₂O/Sreactor/available Temp. Time mol/mol mol/mol kg/mol mol/mol mol/mol Smol/mol ° C. hr Example 1 1.00 1.02 0.40 1.015 1.50 1.050 220-230 3.0 20.96 0.98 0.40 1.015 1.50 1.020 220-230 3.0 3 1.02 1.04 0.40 1.010 1.501.075 220-260 1.5 Comp. 1 0.83 0.85 0.40 1.015 1.50 0.900 220-230 3.0Example 2 0.90 0.92 0.40 1.015 1.50 1.000 220-230 3.0 3 1.02 1.04 0.401.015 1.50 1.100 220-230 3.0 4 1.00 1.02 0.40 1.015 1.20 1.041 220-2607.0 5 1.00 1.02 0.40 1.015 1.20 1.041 220-260 7.0

TABLE 2 Second-stage polymerization Polymer Comp'd. H₂O/S Temp. TimeYield MV Dimer* Reactivity Volatile mol/mol ° C. hr % Pa · s YI ppm withAS** matter rank Example 1 2.80 260 5.0 90 145 5.8 13 2.5 B 2 2.80 2605.0 90 125 5.5 21 2.3 B 3 2.80 260 5.0 88 110 6.0 25 2.2 B Comp. 1 2.80260 5.0 Decomposed — — — — Example 2 2.80 260 5.0 90 90 6.0 50 1.3 C 32.80 260 5.0 70 90 5.9 66 2.0 C 4 — — — 85 130 9.0 85 1.8 C 5 — — — 9595 12.0 117 1.5 DNote:*Dimer: Bis(4-chlorophenyl)sulfide**AS: Aminosilane(γ-aminopropyltriethoxysilane)

INDUSTRIAL APPLICABILITY

According to the present invention, there can be provided productionprocesses of PASs, by which an alkali metal hydrosulfide and an alkalimetal hydroxide can be used in combination as materials for a sulfursource to stably conduct a polymerization reaction, and polymersextremely low in the content of bis(4-chlorophenyl) sulfide that is animpurity secondarily produced upon the polymerization reaction,excellent in reactivity to silane coupling agents such as aminosilane,little in volatile matter in a compound and good in color tone can beprovided.

According to the present invention, there can also be provided PASs lowin the content of bis(4-chlorophenyl) sulfide. According to the presentinvention, there can further be provided PASs excellent in reactivity tosilane coupling agents such as aminosilane.

1. A poly(arylene sulfide) having a bis(4-chlorophenyl) sulfide content lower than 50 ppm as determined by a gas chromatographic analysis.
 2. A poly(arylene sulfide) having a ratio (MV2/MV1) of a melt viscosity value (MV2) of the poly(arylene sulfide) after a reaction with aminosilane to a melt viscosity value (MV1) before the reaction exceeding 2.0 as measured at a temperature of 310° C. and a shear rate of 1,216 sec⁻¹.
 3. A poly(arylene sulfide) having a bis(4-chlorophenyl) sulfide content lower than 50 ppm as determined by a gas chromatographic analysis, a ratio (MV2/MV1) of a melt viscosity value (MV2) of the poly(arylene sulfide) after a reaction with aminosilane to a melt viscosity value (MV1) before the reaction exceeding 2.0 as measured at a temperature of 310° C. and a shear rate of 1,216 sec⁻¹, and a yellow index of at most
 10. 4. The poly(arylene sulfide) according to claim 3, wherein the bis(4-chlorophenyl) sulfide content is at most 30 ppm, the ratio (MV2/MV1) is 2.1 to 3.0, and the yellow index is at most
 7. 5. A process for producing a poly(arylene sulfide) by polymerizing a sulfur source and a dihalo-aromatic compound in an organic amide solvent, which comprises the respective steps of: (1) a dehydration step of heating and reacting a mixture containing the organic amide solvent, an alkali metal hydrosulfide and an alkali metal hydroxide in a proportion of 0.95 to 1.05 mol per mol of the alkali metal hydrosulfide to discharge at least a part of a distillate containing water from the interior of the system containing the mixture to the exterior of the system, (2) a charging step of adding an alkali metal hydroxide and water to the mixture remaining in the system after the dehydration step, as needed, to control the total number of moles of the number of moles of an alkali metal hydroxide formed with hydrogen sulfide formed upon the dehydration, the number of moles of the alkali metal hydroxide added prior to the dehydration and the number of moles of the alkali metal hydroxide added after the dehydration, and the number of moles of water so as to amount to 1.00 to 1.09 per mol of a sulfur source (hereinafter referred to as “charged sulfur source”) including the alkali metal hydrosulfide existing in the system after the dehydration and to 0.5 to 2.0 per mol of the charged sulfur source, respectively, (3) a first-stage polymerization step of adding a dihalo-aromatic compound to the mixture to subject the sulfur source and the dihalo-aromatic compound to a polymerization reaction at a temperature of 170 to 270° C., thereby forming a prepolymer that a conversion of the dihalo-aromatic compound is 50 to 98%, and (4) a second-stage polymerization step of controlling the amount of water in the reaction system after the first-stage polymerization step so as to bring about a state that water exists in a proportion of more than 2.0 mol, but up to 10 mol per mol of the charged sulfur source, and heating the reaction system to 245 to 290° C., thereby continuing the polymerization reaction.
 6. The production process according to claim 5, wherein in the dehydration step, the alkali metal hydrosulfide and the alkali metal hydroxide are supplied as respective aqueous mixtures, and a mixture containing them is heated.
 7. The production process according to claim 5, wherein in the dehydration step, the mixture is heated to a temperature of 100 to 250° C.
 8. The production process according to claim 5, wherein in the charging step, the total number of moles of the alkali metal hydroxide is controlled so as to amount to 1.01 to 1.08 mol per mol of the sulfur source including the alkali metal hydrosulfide.
 9. The production process according to claim 5, wherein in the charging step, the total number of moles of the alkali metal hydroxide is controlled so as to amount to 1.015 to 1.075 mol per mol of the sulfur source including the alkali metal hydrosulfide.
 10. The production process according to claim 5, wherein in the first-stage polymerization step, a prepolymer having a melt viscosity of 0.5 to 30 Pa·s as measured at a temperature of 310° C. and a shear rate of 1,216 sec⁻¹ is formed.
 11. The production process according to claim 5, which further comprises, after the second-stage polymerization step, (5) a separation step of separating a polymer formed from a reaction mixture containing the polymer, and (6) a washing step of washing the polymer thus separated with an organic solvent.
 12. The production process according to claim 11, wherein in the separation step, the polymer is separated from the reaction mixture by sieving.
 13. The production process according to claim 11, wherein the organic solvent used in the washing step is acetone.
 14. The production process according to claim 5, which provides a poly(arylene sulfide) having a bis(4-chlorophenyl) sulfide content lower than 50 ppm as determined by a gas chromatographic analysis.
 15. The production process according to claim 5, which provides a poly(arylene sulfide) having a ratio (MV2/MV1) of a melt viscosity value (MV2) of the poly(arylene sulfide) after a reaction with aminosilane to a melt viscosity value (MV1) before the reaction exceeding 2.0 as measured at a temperature of 310° C. and a shear rate of 1,216 sec⁻¹.
 16. The production process according to claim 5, which provides a poly(arylene sulfide) having a yellow index of at most
 10. 